Saudi Arabian troops arrive in Bahrain to prop up the monarchy against widening demonstrations. Photograph: Ammar Rasool/APAimages/Rex Features

While much of the world has been preoccupied with questions about a no-fly zone over Libya, Arab Gulf states have been busy establishing what might be called a "no-protest zone" in the Arabian peninsula.

Last week Saudi Arabia took an uncompromising stand against demonstrations on its own territory, declaring them both illegal and un-Islamic. Then, on Monday, it sent troops into Bahrain to assist the regime in quelling protesters there. The Saudis justified their action under a security agreement dating back to the Iran-Iraq war of the 1980s and known as Peninsula Shield.

This agreement, which involves the six Gulf Co-operation Council (GCC) countries (Saudi Arabia, Bahrain, the UAE, Oman, Kuwait and Qatar), resulted in the creation of a joint military force intended to protect its members against external threats. As a communique from the GCC interior ministers put it in 1982: "Any aggression on a member state is aggression against the other states, and facing aggression is considered a joint responsibility."

The statement added: "Interference from any entity in the internal affairs of one of the member states is interference in the internal affairs of all the nations of the council."

There was no suggestion at the time that Peninsula Shield forces would be used to protect unrepresentative Gulf regimes from "aggression" or "interference" by their own citizens – and yet this is what has now happened.

Although Saudi Arabia's Peninsula Shield forces appear not to have directly attacked demonstrators in Bahrain – they are supposedly there to protect key parts of the infrastructure – their presence at the very least facilitates the suppression by relieving Bahraini forces of other duties.

Trying to justify this under the terms of Peninsula Shield is certainly ironic, considering that interference in the internal affairs of member states is one of the things the force was set up to guard against, but it becomes a little easier if the Bahraini protesters are characterised as agents of a common enemy: Iran. That can only be achieved by treating the protests as fundamentally sectarian – Shia versus Sunni rather than people versus government.

Religious differences clearly play a big part in Bahrain. After all, the kingdom has a Shia majority ruled by a Sunni minority. Shia Muslims account for most of the protesters, partly because they are the majority and also because they have more to complain about. But, as Bahraini commentator Tahiyya Lulu has pointed out in a couple of recent articles, the pro-reform demonstrators cover a wide spectrum that transcends the sectarian divide.

The effect of the Saudi intervention is to sectarianise the conflict more than it need have been and, in effect, to prevent any accommodation between the rulers of Bahrain and the protesters.

"We're not going in [to Bahrain] to shoot people, we're going in to keep a system in place," a Saudi official was quoted as saying in the Washington Post. An official from the UAE put it even more bluntly: "We and the Saudis will not accept a Shi'ite government in Bahrain."

In other words, as far as the GCC countries are concerned, democracy or majority rule can never be allowed there.

This is unbelievably short-sighted. The majority of Bahrain's population cannot be kept marginalised for ever, and the sooner change gets under way the better it will be for everyone. Instead, the regime is being pushed into an intransigent stance which, in the longer term, may well seal its fate.

The Saudis, meanwhile, continue to store up trouble for themselves in their treatment of the Shia communities back home.

Unsurprisingly, the US has been less critical of all this than it has been in relation to Gaddafi's behaviour in Libya, though on Wednesday secretary of state Hillary Clinton came out with her strongest comments so far, saying that Bahrain is on "the wrong track".

"With the Gulf countries, we've made it very clear that there cannot be a security answer to what are legitimate political questions," she said.

As always, the US continues to fret about stability among its allies but increasingly it seems to be recognising – unlike Gulf rulers themselves – that radical change is inevitable and that the wisest course is not to stand in its way but to try to minimise the turmoil when it happens.